Bug 23859: Make POST add the Location header on cities endpoint

Bug 23859: Make POST add the Location header on cities endpoint

According to the coding guidelines, this endpoint should be adding the
Location header on POST actions.

To test:
1. Apply the tests patch
2. Run:
    $ kshell
    k$ prove t/db_dependent/api/v1/cities.t
=> FAIL: Tests fail!
3. Apply this patch
4. Repeat (1)
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>